Latch mechanism for lift trucks



Aug. 29, 1967 D. J. M NEELEY LATCH MECHANISM FOR LIFT TRUCKS Filed May 13, 1966 4 Sheets-Sheet 1 FIG?) FIG. I0

INVENTOR DANIEL JAMES MC NEELEY BYW-{m ATTORNEY Aug. 29, 1967 D. J. M NEEL EY LATCH MECHANISM FOR LIFT TRUCKS Filed May 13, 1966' 4 Sheets-Sheet 2 FIG. 32

INVENTOR DANIEL JAMES MC NEELEY BY WQKWORNEY Aug. 29, 1967 D. J. MCNEELEY LATCH MECHANISM FOR LIFT TRUCKS 7 Filed May 13, 1966 4 Sheets-Sheet 3 INVENTOR DANIEL JAMES MC NEELEY Aug. 29, 1967 D. J. M NEELEY LATCH MECHANISM FOR LIFT TRUCKS 4 Sheets-Sheet 4 Filed May 13, 1966 134 I36 I38 I37 FIG. 25

89 l56 9O FIG.3O

FIG. 29

INVENTOR DANIEL JAMES MC NEELEY TORNEY United States Patent 3,338,335 LATCH MECHANISM FOR LIFT TRUCKS Daniel James McNeeley, Cleveland, Ohio, assignor to Otis Elevator Company, New York, N.Y., a corporation of New Jersey Filed May 13, 1966, Ser. No. 549,978 11 Claims. (Cl. 187-9) ABSTRACT OF THE DISCLOSURE A latch mechanism including first, second and third relatively rotatable members one of which may be fastened to one component of a lift truck while the other two may be engaged from time to time by other components and in which the second and third members each have a reference position with respect to the first member from which position either one but not both simultaneously may be displaced.

This invention relates generally to lift trucks and partrcularly to latching mechanisms which insure the proper sequence of operation of the load carriage and movable upright assemblies.

A typical lift truck includes a pair of stationary, generally vertical uprights, one or more pairs of movable uprights, a load supporting carriage movable along the uprights, and a lifting mechanism for raising and lowering the load carriage and movable uprights in a predetermined sequence. It is desirable that during operation the selected predetermined sequence of operations be maintained during both lifting and lowering. To this end, many kinds of latch mechanisms have been proposed in the past which selectively lock together the stationary uprights, the movable uprights, the lifting mechanism, and the load carriage in various combinations during various portions of the lifting and lowering cycles. However, none of these latching arrangements have been entirely satisfactory.

It is a general object of the present invention to provide an improved latching mechanism for an industrial lift truc Another object is to provide a latching mechanism which operates properly with a minimum amount of adjustment during installation.

Another object is to provide a latching mechanism in which normal wear during use has little or no effect on proper operation.

Another object is to provide a sturdy mechanism which is not easily damaged.

Another object is to provide a latch mechanism in which a first member may readily be unlatched from a second member and latched to a third member.

Briefly stated, the invention comprises a first member formed with an aperture therethrough which member is interposed between and in sliding engagement with second and third members each formed with a depression in that surface adjacent to the first member. Alocking element is positioned in the aperture and is of such length as to necessarily extend into the depression in one or the other of the second or third members thereby locking one or the other to the first member.

As applied to a lift truck, all three members are preferably rotatable about a common axis. The first member is non-rotatably fastened to one portion of the truck, such as the inner uprights. The second and third members are each formed with a radially extending fork, which forks are selectively engaged by studs or the like fastened to other portions such as the outer uprights, the intermediate uprights, the lifting mechanism, and the load carriage. By this arrangement, the inner uprights may, for example,

3,338,335 Patented Aug. 29, 1967 be locked successively to the outer uprights, the lifting mechanism, and the load carriage.

For a clearer understanding of the invention, reference may be made to the following detailed description and the accompanying drawing, in which:

FIGURE 1 is a fragmentary elevation view of a lift truck;

FIGURE 2 is a schematic view of one form of a two stage mast assembly, lifting mechanism and load carriage for a lift truck;

FIGURES 3, 4 and 5 are schematic views similar to FIGURE 2 showing the same parts in difierent relative positions;

FIGURE 6 is a schematic cross section view illustrating the principles of the latching mechanism of the invention;

FIGURE 7 is an exploded view of a preferred embodiment of a latch according to the invention;

FIGURE 8 is an isometric view showing how the latch of FIGURE 7 may be mounted;

FIGURE 9 is an elevation view with parts broken away, taken from the side remote from the viewer in FIGURE 8, showing details of the mounting arrangement;

FIGURE 10 is a plan view of the latch showing the relative positions of studs which cooperate therewith;

FIGURES 11 to 15 inclusive are schematic views in elevation showing the operation of the latch as applied to a mast assembly such as that depicted in FIGURES 2 to 5 inclusive;

FIGURES 16, 17 and 18 are schematic views of another form of two stage mast assembly, showing the parts in various different relative positions;

FIGURES 19, 20 and 21 are schematic views in elevation showing the operation of the latch as applied to a mast assembly such as that depicted in FIGURES 16, 17 and 18;

FIGURES 22 to 27 inclusive are schematic views showing one form of a triple stage mast assembly, the various views showing the parts in different relative positions;

FIGURES 28, 29 and 30 are schematic views in elevation showing the operation of a second latch which may be used with a mast assembly such as that depicted in FIGURES 22 to 27 inclusive;

FIGURE 31 is an elevation view of a modified form of latch mechanism; and

FIGURE 32 is a cross section view of another modification.

Referring first to FIGURE 1, there is shown a portion a lift truck 31 including wheels 32, a mast structure 33,

and a load carriage 34 to which are attached lifting forks 35. In FIGURE 1, the lift carriage 34 is shown in a slightly raised position so that the forks 35 are raised above the ground level 36. The mast assembly 33 may, for example, comprise a pair of outer stationary uprights and a pair of inner uprights along which the load carriage 34 is movable and which are movable longitudinally with respect to the outer uprights. The assembly 33 may also include a pair of intermediate uprights interposed between the outer and inner uprights. A truck such as the truck 31 usually includes a power actuated lifting mechanism such as an hydraulic ram (not shown in FIG- URE 1) which typically acts through an arrangement of chains and pulleys to raise the carriage with respect to the movable uprights and to raise the movable uprightswith respect to the stationary uprights. The constructional details of the mast assembly and lifting mechanism are not a part of the present invention except insofar as such details include the mounting of the latch or latches and the provision of studs, projections and the like which cooperate with the latches as will be more fully explained. There are many possible different ar rangements of uprights, ram mechanisms, chains and pulleys, and the present invention is applicable to most, if not all, of them. A few exemplary mast assemblies and lifting mechanisms will be described and illustrated schematically.

Referring now to FIGURE 2, an outer, generally vertical, stationary upright 41 is shown as integral with or fastened to a generally horizontal frame portion 42 of the truck which portion is supported by the wheels (not shown) a few inches above the floor or ground level 36. An hydraulic ram mechanism 43 rests on the portion 42 and includes a piston rod 44 (shown in FIGURES 3, 4 and on which is mounted a crosshead 45 which rises as fluid under pressure is admitted to the ram mechanism 43. The crosshead 45 has a pulley 46 rotatably mounted thereon over whichpasses a chain 47 one end of which is held stationary, for example by fastening to the frame portion 42, while the other end is fastened to the load carriage 34.

An inner upright 48 rests on the frame portion 42 and includes portions 51 and 52 which cooperate with and are engaged by the crosshead 45 and a portion 53 of the carriage 34 respectively during operation as will be more fully described. In the position of the parts shown in FIGURE 2, the crosshead 45, the inner uprights 48 and the carriage 34 are in their lowermost positions with the forks 35 at ground level. It is to be understood that the showing of FIGURE 2 is highly schematic and that it is contemplated that the outer upright 41, the inner upright 48, the load carriage 34 and the ram mechanism 43 be of conventional construction.

In operation, fluid under pressure is admitted to the ram mechanism 43 whereupon the crosshead 45 rises thereby raising the carriage 34 at twice the rate of rise of the crosshead. As the carriage 34 and crosshead 45 continue to rise, they soon reach the positions shown in FIGURE 3 at which the crosshead engages the portion 51 of the upright 48. Thereafter the crosshead 45 raises the upright 48 directly while the carriage 34 continues to rise relative to the upright 48 until the position of FIGURE 4 is reached at which position the portion 53 of the carriage 34 engages the portion 52 of the upright 48. Thereafter the carriage 43 raises the upright 48 above the top of the crosshead 45 until the maximum height is reached at the position shown in FIGURE 5.

To lower the load, the fluid is released from the ram 43 whereupon the sequence of operations should be the opposite of that just described. When in the position of FIGURE 5, release of fluid pressure should cause the carriage 34 and the upright 48 to descend together. However, if the upright should bind, as sometimes happens, the carriage may descend a short distance leaving the upright elevated but without substantial support. A subsequent jar may cause the upright to break loose and drop suddenly, thereby endangering both the mast assembly and the load. A similar malfunction could occur with the parts in any position between that of FIGURES 3 and 4, if the upright 48 should bind, in which case the crosshead 45 might descend leaving the upright without substantial support. The latch mechanism of the present invention prevents such malfunctions.

Referring now to FIGURE 6, there are shown first, second and third members 56, 57 and 58 which may be flat metal plates. These plates are mounted to be held in sliding engagement with each other. For example, regarding the plate 56 as stationary, the plates 57 and 58 are freely movable from right to left, as viewed in FIG- URE 6, but cannot move up and down so as to become disengaged from each other. The plate 56 is formed with an aperture 59 extending completely therethrough while the plates 57 and 58 are formed with shallow depressions 61 and 62 respectively in those surfaces which are in engagement with the plate 56. A ball 63 is placed in the aperture 59 and has a diameter greater than the thickness of the plate 56 but no greater than this thickness plus the depth of one of the depressions 61 or 62. The ball 63 therefore necessarily extends into one or the other of the depressions 61 or 62. The position of the plate 57 illustrated in FIGURE 6 with the depression 61 aligned with the aperture 59 is designated the reference position of the plate 57. Similarly, the position of the plate 58 with the depression 62 aligned with the aperture 59 is designated the reference position of the plate 58. It is apparent that either one but not both of the plates 57 and 58 may be moved from its reference position at any one time. This is so because as soon as one of the plates is moved the ball 63 extends into the depression in the other plate thereby locking it in position.

The principles illustrated in FIGURE 6 in which the three members are substantially planar plates and in which the motion is translatory, can be extended to other shapes and to rotary motion. For example, the three members may be discs rotatable about a common axis. As another example, the three members may be cylindrical, or even spherical, and the motion control may be either axial or rotary. Additionally, the ball may in some cases be replaced with a cylindrical roller and may in other cases be replaced with an elongated pin with rounded ends. In any case, the fundamental mode of operation is the same. Regarding the inner member as stationary, one and only one of the other two members may be displaced from its reference position at any one time.

Referring to FIGURE 7, a sleeve 65 is formed with an axially extending aperture or slot 66 on one end and is provided with a flange or collar 67 in approximately the middle. The other end 68 of the sleeve 65 is formed with an aperture 69 and is used for mounting the latch mechamsm.

A cylindrical roller 71 is positioned within the aperture 66 and has a length slightly less than the length of this aperture and a diameter greater than the thickness of the sleeve.

Another sleeve 73 surrounds the sleeve 65 with a freely sliding fit and is formed with an axially extending elongated depression or groove 74 on the inside surface which groove cooperates with the aperture 66 and the roller 71. A fork comprising two axially aligned tines 75 and 76 is formed integrally with the sleeve 73 and extends approximately radially therefrom. A pin or rod 77 is welded or otherwise rigidly fastened to the exterior of the sleeve 73 as shown to constitute a stop member.

A hub 81 fits within the sleeve 65 and is of such length as to extend throughout the entire sleeve including the portion 68. The diameter of the hub 81 is selected to form a freely sliding fit with the interior of the sleeve 65. The hub 81 is formed with an elongated, axially extending depression or groove 82 on the outer surface which groove cooperates with the aperture 66, the roller 71 and the groove 74. The hub 81 is also formed with a circumferential groove 83 which is positioned to be axially aligned with the aperture 69 in the sleeve portion 68. The hub 81 is also formed with two additional shallow circumferential grooves 84 and 85 which aid in distributing a lubricant. The hub 81 includes an enlarged diameter portion 86 at one end, integral therewith or rigidly fastened thereto. The portion 86 is formed with a double fork including four tines 87, 88, 89 and 90, extending approximately radially therefrom. The tines 87 and 88 are axially aligned with each other and constitute a first fork while the tines 89 and 90 are axially aligned with each other and constitute a second fork axially displaced from the first fork.

The latch mechanism is assembled by telescoping the parts from the exploded position shown in FIG. 7. When so assembled, the grooves 74 and 82 are both axially aligned with the aperture 66. The angular position of the sleeve 73 at which the groove 74 is angularly aligned with the aperture 66 is denoted the reference position of the sleeve 73. Similarly, the angular position of the hub 81 at which the groove 82 is angularly aligned with the aperture 66 is denoted the reference position of the hub 81. As previously mentioned, the diameter of the roller 71 is greater than the thickness of the sleeve 65 and is preferable approximately equal to but not greater than this thickness plus the depth of one of the grooves 74 or 82. Thus it is apparent that either the sleeve 73 or the hub 81, but not both at once, can be displaced from their respective reference positions. For example, if the sleeve 73 be rotated away from its reference position, the roller 71 will be forced into the groove 82 thereby holding the hub 81 as stationary with respect to the sleeve 65. If the sleeve 73 be returned to its reference position, then the hub 81 may be displaced in which case the roller 71 will be forced into the groove 74 thereby locking the sleeve to the sleeve 65.

FIGURES 8 and 9 show a typical mounting arrangement for a latch. The member 93 is intended to represent any structural member fastened to some portion of the mast assembly such as a cros piece rigidly fastened to the inner upright or to the intermediate upright. A plate like bracket 94 is positioned in a generally vertical plane and rigidly fastened to the member 93. The bracket 94 has a horizontal bore of such diameter as to snugly receive the sleeve portion 68. A bolt 95 is threaded into a tapped hole in the bottom of the bracket 94 and extends into the aperture 69, thereby fastening the sleeve 65 rigidly. The bolt 95 is held in place by a lock nut 96.

Also shown in FIGURES 8 and 9 is a pin or rod 97 rigidly fastened to the outside of the enlarged portion 86 to constitute a stop member. The angular position of the aperture 69, the aperture 66 and the grooves 74 and 82 are selected so that the sleeve 73 and the hub 81 are in their reference positions when their corresponding forks are approximately horizontal. Displacement of either of the members from the horizontal position is limited to about 45 degrees as shown in FIGURE 9 where the stop members 77 and 97 have engaged each other. FIG- URE 8 also shows a grease fitting '98 which communicates by interior passageways with the grooves 84 and 85.

Let us assume that the latch mechanism is to be used with a mast assembly such as that illustrated in FIGURES 2 to 5 inclusive. In such a case, the member 93 of FIG- URES 8 and 9 represents a structural member such as a cross piece fastened to the inner upright 48 of FIGURES 2 to 5 and the sleeve 68 is fastened thereto by means of the bracket 94. A bracket 101, FIGURE 10, is fastened to the outer upright and carries a stud or other projection 102 which is positioned to cooperate with the tines 87 and 88. A bracket 103 is fastened to the load carriage and a stud 104 projects therefrom in such a position as to cooperate with the tines 89 and 90. A bracket 105 is fastened to the crosshead and a stud 106 projects therefrom in such position as to cooperate with the tines 75 and 76.

The sequence of operations is shown in FIGURES 11 to 15 inclusive. With the parts completely lowered, as shown in FIGURE 2, the latch is in the position shown in FIGURE 11 with the tines 87 and 88 approximately horizontal and embracing the stud 102 (fastened to the outer upright). At this time the tines 75 and 76 are inclined downward at an angle of approximately 45 degrees to which they are limited by the engagement of stop members 77 and 97 as shown. Since these tines are displaced from their reference position, the fork comprising tines 87 and 88 cannot move from its reference position and therefore the outer upright is locked to the inner upright. The studs 104 and 106 are below the level of the latch and do not affect it at this time.

As fluid under pressure is admitted to the ram 43, the crosshead 45 rises, raising the stud 106. The stud 106 enters the space between the tines 75 and 76, engages the tine 76, and rotates it to the horizontal position as shown in FIGURE 12. This horizontal position is reached just as the crosshead 45 engages the portion 51 of the inner upright as shown in FIGURE 3. Both forks are now in their reference positions and either one can be displaced therefrom. As the crosshead 45 rises, it raises the inner upright and the latch mechanism along with it causing the tine 88 to bear against the stud 102. As the latch rises, the tines 87 and 88 are rotated counterclockwise, as viewed in FIGURE 12, thereby releasing the stud 102 which remains below as the latch rises. Rotation of the tines 87 and 88 away from their reference position locks the tines 75 and 76 in the horizontal position thereby locking the stud 106 and the crosshead 45 to the inner upright. This position of the parts is illustrated in FIG- URE 13. Rotation of the tines 87 and 88 is limited by the engagement of the stop members 77 and 97. The latch remains in the position shown in FIGURE 13 as the crosshead 45 rises from the position shown in FIGURE 3 to that shown in FIGURE 4.

If it is desired to lower the load carriage when in any position between those shown in FIGURES 3 and 4, fluid pressure is released from the ram 43 whereupon the crosshead 45 starts to descend. If the inner upright 48 should bind, the stud 106 would bear against the time 75 thereby pulling the latch mechanism and the inner upright down.

Assuming that it is desired to raise the load carriage further, additional fluid is admitted to the ram 43 whereupon the crosshead 45 rises thereby raising the inner upright and the load carriage. Soon the stud 104 fastened to the load carriage rises above the stud 102 fastened to the outer upright as shown in FIGURE 13. As the position shown in FIGURE 4 is approached, the stud 104 enters the space between the tines 89 and thereby rotating these tines clockwise as viewed in FIGURE 13. The relative positions of the parts are selected so that the tines 89 and 90 reach the horizontal position as shown in FIGURE 14 just as the portion 53 of the load carriage engages the portion 52 of the inner upright as shown in FIGURE 4. Further upward movement of the crosshead 45 raises the carriage at twice the rate of rise of the crosshead thereby raising the inner upright 48 above the crosshead. At the same time the tine 75 engages the stud 106 thereby rotating the tines 75 and 76 clockwise so as to release the stud 106. Since the tines 75 and 76 have been rotated away from their reference position, the tines 89 and 90 are locked in the horizontal position shown in FIGURE 15 thereby locking the stud 104 and the load 'carriage 34 to the inner upright. It is obvious that the load carriage cannot descend without pulling the inner upright down with it.

Another kind of mast arrangement is shown in FIG- URES 16, 17 and 18. An outer stationary upright 111 is fastened to a horizontal frame portion 112 which is held a few inches above the ground by wheels of the truck (not shown). A ram assembly 113 includes a first extensible cylinder 114 and a second extensible cylinder 115. A crosshead 116 is mounted on top of the cylinder 115. A pulley 117 is rotatably mounted on the crosshead 116. An inner movable upright 118 is formed with a projection 119 which cooperates with a similar projection 121 formed on a load carriage 122. Two pulleys, 123 and 124, are fastened near the top and bottom respectively of the inner movable upright 118. A chain 125 has one end held stationary as by fastening to the frame portion 112 and passes over the pulley 117 on the crosshead, under the lower pulley 124 on the inner upright, over the upper pulley 123 on the inner upright, and thence to the load carriage 122 to which the other end is fastened. The carriage 122 includes a pair of load lifting forks 126.

The latch of the present invention may also be applied to the mast assembly and lifting arrangement shown in FIGURES 16, 17 and 18. As before, the member 93 of FIGURES 8 and 9 may be regarded as a cross piece fastened to the inner-upright. However, the arrangement of the studs is just a bit ditferent.

Referring to FIGURES 19, 20 and 21, the reference character 128 represents a stud fastened to the outer upright 111. The reference character 129 represents a stud fastened to the load carriage 122. With the carriage lowered to the ground, as shown in FIGURE 16, the stud 128 is between the tines 89 and 90 as shown in FIGURE 19. The tines 75 and 76 are inclined downwardly as shown so that the tines 89 and 90 are locked in their horizontal position. Therefore, as the load carriage 122 is raised from the position of FIGURE 16 to the position of FIGURE 17, the inner uprights cannot rise because they are locked to the outer uprights. As the position of FIGURE 17 is approached, the stud 129 enters the space between the tines 75 and 7 6, rotating them counterclockwise and reaching the horizontal position as shown in FIGURE 20 just as the projection 121 on the carriage 122 engages the projection 119 on the inner upright 118 as shown in FIGURE 17. Continued upward movement of the crosshead 116 raises the load carriage 122 and the .inner upright 118 together. The tine 90 engages the stud 128 as the latch mechanism rises thereby rotating the tines 89 and 90 counterclockwise and releasing the stud 128 as shown in tines 89 and 90 are rotated slightly away from the horizontal, the tines 75 and 76 are locked in their reference position thereby locking the stud 129 and the load carriage 122 to the inner upright 118. It is apparent that when the parts are in the position shown in FIGURE 18, the load carriage cannot be lowered without also lowering the inner upright 118.

It is to be noted that with the mast assembly and lifting mechanism of FIGURES 16, 17 and 18, there is but one look transferring operation as the carriage is raised from the ground level to its highest position. The inner upright is at first locked to the outer upright and the single transferring operation occurs as the inner upright is released from the outer upright and locked to the carriage. As shown in FIGURES 19 to 2.1, the two pairs of tines 75, 76, 89, 91) are used while the remaining pair 87, 88 is superfluous and could be omitted. However, the preesnce of these tines, even though not used, does not harm.

A triple stage mast assembly and lifting mechanism is shown schematically in FIGURES 22 to 27 inclusive, which show the parts in various positions from that of FIGURE 22 in which the load carrying forks are at ground level through successively higher positions of the forks to and including the position of maximum height as shown in FIGURE 27. A generally vertical outer, stationary upright 131 is joined to a horizontal portion 132 of the truck which portion is supported a few inches above ground level 36 by wheels (not shown in these figures). An intermediate upright 133 is constructed and arranged in any conventional manner to be readily movable longitudinally along the outer upright 131. The intermediate upright 133 includes an abutment 134 rigidly fastened thereto. An inner movable upright 135 is constructed in a conventional. manner to be readily movable longitudinally with respect to the intermediate upright 133. The inner upright 135 includes generally horizontal abutments 136 and 137 rigidly fastened thereto. Two pulleys 138 and 139 are rotata-bly mounted near the top and near the bottom of the inner upright 135 respectively. A load carriage 141 is mounted in any conventional manner to be readily movable longitudinally along the inner upright 135. The carriage 141 includes a generally horizontal abutment 142 and also has load lifting forks 143 fastened thereto. A hydraulic ram mechanism, indicated generally by the reference character 144, includes a first extensible cylinder 145 and a second extensible cylinder 146. The cylinder 146 carries near its top a crosshead 147 which in turn includes generally horizontal abutments 148 and 149, A pulley 151 is rotatably mounted on the crosshead 147. A chain 152 has one end fastened to a stationary portion of the structure such as the horizontal portion 132 of the frame and passes over the pulley 151, under the pulley 139, over the pulley 138,

FIGURE 21. As soon as the 8 and has its opposite end fastened to the load carriage 141.

Let us follow the sequence of operations when the lifting forks are to be raised from the ground level 36 as shown in FIGURE 22 to their maximum height as shown in FIGURE 27. As fluid under pressure is admitted to the ram mechanism 144, the first extensible cylinder 145, and the second extensible cylinder 146 rise together thereby raising the crosshead 147. The chain 152 and the pulleys 151, 139 and 138 operate in a well known manner to raise the load carriage 141 at a rate twice that of the crosshead 147. The carriage 141 alone rises, the inner upright 135 and the intermediate upright 133 remaining stationary until the carriage 141 has nearly reached the top of the inner upright 135, as shown in FIGURE 23, at which position the abutment 149 on the crosshead 147 engages the abutment 136 which is fastened to the inner upright 135. The inner upright 135 now rises at the same rate as the crosshead 147 while the load carriage 141 continues to rise relative to the inner upright 135.

Soon after the position of FIGURE 23 is passed, the abutment 148 on the crosshead 147 engages the abutment 134- which is fastened to the intermediate upright 133. This position is shown in FIGURE 24 and as this position is passed, both the inner upright 135 and the intermediate upright 133 are raised directly by the crosshead while the load carriage 141 continues to rise faster than the crosshead. The load carriage 141 soon overtakes the inner upright 135 as shown in FIGURE 25 at which position the abutment 142 on the load carriage engages the abutment 137 on the inner upright. The load carriage 141, which is rising at twice the speed of the crosshead, now raises the inner upright 135 above the crosshead as shown in FIGURE 26. At approximately the position shown in FIGURE 2.6, the first extensible cylinder 145 has reached its maximum limit of travel and the second extensible cylinder 146 extends relative to the first. The crosshead 147 and the intermediate upright 133 rise together while the load carriage 141 and the inner upright 135 rise together at a rate twice that of the rise of the crosshead.

The latch mechanism may be applied to the mast assembly shown in FIGURES 22 to 27 in much the same way as it is applied to the mast assembly of FIGURES 2 to 5. In FIGURES 8 and 9, the member 93 is regarded as a structural member such as a cross piece connected rigidly to the inner upright 135 of FIGURES 22 to 27. In FIGURES 11 to 15, the reference character 102 may now represent a stud connected to the outer upright 131; the reference character 104 may represent a stud connected to the carriage 141; and the reference character 106 may represent a stud connected to the crosshead 147. With the forks 143 at ground level, as shown in FIGURE 22, the stud 102 is positioned between the tines 87 and 88, as shown in FIGURE 11, thereby latching the inner upright 135 to the outer upright 131. When the crosshead 147 engages the inner upright, as shown in FIGURE 23, the stud 1116 enters the space between the tines 75 and 76, thereby releasing the outer upright from the inner and in turn latching the inner upright to the crosshead, as shown in FIGURES 12 and 13. When the load carriage 141 overtakes the inner upright 135, as shown in FIGURE 25, the stud 104 enters the space between the tines 89 and thereby releasing the inner upright from the crosshead 147 locking it instead to the load carriage 141 as shown in FIGURES 14 and 15. The latch remains in this position throughout the remainder of the lifting cycle.

With the triple stage rnast asembly illustrated in FIG- URES 22 to 27, it is prefered to provide a second latch for the intermediate upright. With reference to this latch, the member 93 of FIGURES 8 and 9 represents a structural member such as a cross piece rigidly fastened to the intermediate upright 133. In FIGURES 28, 29 and 30, the reference character 156 represents a stud fastened to the outer upright 131 and the reference character 157 represents a stud fastened to the crosshead 147. The latch mech- 9 anism maybe one in which but a single pair of tines are fastened to the enlarged portion 86 (FIGURE 7) but for simplicity it will be assumed that the mechanism is the same as illustrated in FIGURE 7.

With the forks on the ground, as illustrated in FIG- I URE 22, the stud 156 lies between the tines 89 and 90 While the tines 75 and 76 are inclined downwardly as shown in FIGURE 28, thereby locking the intermediate upright 133 to the outer upright 131. As the carriage rises, the latch mechanism remains in this position until the abutment 148 on the crosshead engages the abutment 134 on the intermediate upright, as shown in FIGURE 24, in which position the stud 157 enters the space between the tines 75 and 76 bringing them to the horizontal position as shown in FIGURE 29 just as the above mentioned abutments come together. As the crosshead rises, the stud 156 is released and the stud 157 locked to the intermediate upright as shown in FIGURE 30. These parts remain in this position throughout the remainder of the lifting cycle.

With the parts in the position shown in FIGURE 27, let it be assumed that it is desired to lower the load carriage. As fluid pressure is released from the ram 144, the load carriage descends. The inner upright 135 cannot remain elevated because it is locked to the carriage 141 and must necessarily descend therewith until the position of FIGURE 25 is reached at which position the inner upright 135 is unlatched from the load carriage 141 and latched to the crosshead 147. Thereafter, as the crosshead descends it must necessarily bring the inner upright 135 down with it until the position of FIGURE 23 is reached at which position the inner upright is unlatched from the crosshead and latched to the outer upright 131.

Returning to the position of FIGURE 27, as pressure is released from the ram 144, the crosshead 147 descends and the intermediate upright 133 must necessarily descend with it because it is locked thereto. The intermediate upright remains latched to the crosshead 147 until the position of FIGURE 24 is reached at which position the intermediate upright is unlatched from the crosshead 147 and latched to the outer upright 131.

From the foregoing it will be apparent that applicant has provided an improved latch mechanism, eminently suitable for insuring the proper sequence of operations of various portions of the load lifting mechanism of lift trucks. The mechanism is simple, rugged, and easily installed and adjusted. There are no parts with critical dimensions and accordingly normal wear does not affect operation adversely.

It is to be noted that the same design, or model, of latch mechanism can be used with various mast and load lifting assemblies. Additionally, in the case of triple stage uprights, one latch mechanism can control the inner upright while another similar, or even identical, latch mechanism can control the intermediate upright.

It is also to be noted that a single latch mechanism is used to latch one member, such as the inner upright, suc cessively to various other members, such as the outer upright, the crosshead and the lift carriage. This feature simplifies the problem of releasing one member and latching another at substantially the same time.

It is further to be noted that, although stop members 77 and 97 have been shown to limit the downward movement of the forks, none have been shown to limit upward movement. Such stop members may, of course, be provided if necessary but it frequently happens in practice that the structural member 93, shown in FIGURES 8 and 9, overlies the latch mechanism and serves to limit upward movement of the forks.

When the parts are in their lowermost positions, as shown in FIGURES 11, 19 and 28, the tines 75, 76 are inclined downward from their reference position so as to lock the outer uprights to tines 87, 88 or 89, 90. However, nothing but gravity is holding the tines 75 and 76 in this position since no stud is between them. A similar situation occurs at the uppermost position of FIGURES 15, 21 and 30, as well as at the intermediate position of FIGURE 13 after the mechanism has risen above the stud 102 and before it is engaged by the stud 104. While nothing is likely to displace the tines from their proper positions, and although the force of gravity is ordinarily sufficient to return them to the proper position, it is possible in the position of FIGURE 11 for example, for someone or something to raise the tines 75, 76 sufiiciently so that the stud 106 cannot enter the space between them. Such a condition would obviously lead to a malfunction. However, such a malfunction can be prevented by a slight modification of the latch mechanism such as that shown in FIGURE 31 wherein small lugs 161 and 162 are welded to the tines 75 and 88 respectively. A tension spring 163 is fastened to these lugs and urges the tines together. Therefore, if the tines should be displaced inadvertently, the spring 163 would restore them to their proper position.

Also shown in FIGURE 31 is an alternative form of stop mechanism comprising a roll pin 165 which fits snugly in an aperture in the tine 75 and extends therebeyond so as to engage the enlarged portion 86 when the tines have been urged to the position shown in this figure.

FIGURE 32 shows a further modification in which the sleeve 65 is formed with an additional aperture or slot 66' approximately opposite the slot 66. Similarly, the sleeve 73 and the hub 81 are each formed with corresponding additional depressions or grooves 74' and 82' respectively. An additional roller 71' is positioned in the slot 66' and operates simultaneously and in the same way as the roller 71 thereby sharing the load and decreasing the wear on the .parts. Of course, the use of the additional grooves, slot and roller limits the range of displacements from the reference positions to something less than half a revolution, but for many purposes, such as that described herein, the desired displacement is much less than half a revolution. Indeed, for present purposes, it would be possible to use three or even four rollers, since the maximum displacement is only about forty-five degrees. However, for present purposes, two rollers have been found to .be adequate.

Although a preferred embodiment of the invention has been described in considerable detail for illustrative purposes, many modifications within the spirit of the invention will occur to those skilled in the art. It is therefore desired that the protection afforded by Letters Patent be limited only by the true scope of the appended claims.

What is claimed is:

1. A latch mechanism, comprising,

first, second and third members including generally cylindrical portions positioned concentrically with freely sliding fits for relative rotation about their common axis with said first member interposed between said second and third members,

said first member being formed with an axially elongated radial aperture or slot,

said second and third members each being formed with a groove in that surface adjacent to said first member and axially aligned with said aperture,

said second and third members each having a reference position defined as that angular position at which its groove is angularly aligned with said aperture, and a cylindrical roller positioned principally within said aperture and having a diameter greater than the thickness of said first member but no greater than said thickness plus the depth of one of said grooves,

whereby said roller necessarily extends into at least one of said grooves, and

whereby either said second or said third member but not both simultaneously may be angularly displaced from its reference position,

said first member being provided with the means for fastening an external body rigidly thereto,

said second and third members each being provided with means for engaging other external bodies as they move relative to said first external body,

whereby relative motion among said external bodies is controlled.

2. Apparatus according to claim 1 in which said means for engaging comprise first and second forks fastened to said second and third members respectively and extending approximately radially therefrom.

3. Apparatus according to claim 2 further comprising means for limiting the relative rotation of said second and third members.

4. A lift truck, comprising,

a frame,

a pair of stationary, outer uprights fastened to said frame in an approximately vertical position,

a pair of inner, movable uprights longitudinally extensible with respect to said outer uprights,

a load carriage movable along said inner uprights,

means including a crosshead for raising said carriage with respect to said inner uprights and for raising said inner uprights with respect to said outer uprights,

said means including a portion of said crosshead which is positioned to engage a portion of, and to raise, said inner uprights by upward movement of said crosshead in excess of a predetermined amount above a lowermost position,

a first member including a generally cylindrical sleeve portion formed with a radial aperture therethrough and rigidly fastened to said inner uprights with the cylindrical axis approximately horizontal,

a second member including a generally cylindrical hub portion formed with a depression in the cylindrical surface thereof and positioned within said sleeve portion of said first member with said depression axially aligned with said aperture, said second member including a first radially extending fork having two axially aligned tines,

a third member including a generally cylindrical sleeve portion formed with a depression in the inner surface thereof and positioned surrounding said sleeve portion of said first member with said depression axially aligned with said aperture, said third member including a second radially extending fork having two axially aligned tines,

that angular position of said second member in which said depression in said hub is angularly aligned with said aperture being designated as the reference position of said second member,

that angular position of said third member in which said depression in said inner surface of said sleeve portion is angularly aligned with said aperture being designated as the reference position of said third member,

each of said forks being angularly positioned to be approximately horizontal when its associated member is in its reference position,

a locking element positioned within said aperture and having a dimension in the radial direction which is greater than the thickness of said sleeve portion of said first member but no greater than said thickness plus the depth of one of said depressions so as to necessarily extend into one of said depressions.

whereby but one of said second and third members may be displaced from its reference position at any one time,

stop means for limiting the relative rotation of said second and third members,

a first stud fastened to said outer uprights and positioned so that with said inner uprights fully lowered and said second member in its reference position,

said first stud extends between the horizontally extending tines of said first fork,

whereby said second fork is urged downward thereby locking said inner uprights to said outer uprights, and

a second stud fastened to said crosshead and positioned to enter the space between the tines of said second fork as said crosshead rises and to raise said second fork to a horizontal position substantially as said portion of said crosshead engages said portion of said inner uprights,

whereby continued upward movement of said crosshead raises said inner uprights and rotates said first fork downwardly thereby releasing said first stud and said outer uprights and simultaeously locking said crosshead to said inner uprights.

5. Apparatus according to claim 4 in which said aperture in said first member is axially elongated to form a slot and in which each of said depressions is axially elongated to form a groove and in which said locking element is a cylindrical roller having a length greater than its diameter.

6. Apparatus according to claim 5 in which said means for raising also includes a portion of said carriage positioned to engage a portion of said inner uprights as said carriage reaches the top of said inner uprights and which further comprises a third stud fastened to said load carriage and positioned to enter the space between the tines of said first fork as said load carriage approaches the upper end of said inner uprights and to raise said first fork to a horizontal position substantially as said portion of said carriage engages said portion of said inner uprights,

whereby continued upward movement of said crosshead raises said carriage which in turn raises said inner uprights above said crosshead, simultaneously rotating said second fork downwardly thereby releasing said second stud from said second fork and latching said third stud and said carriage to said inner uprights.

7. Apparatus according to claim 6 in which said aperture in said first member is axially elongated to form a slot and in which each of said depressions is axially elongated to form a groove and in which said locking element is a cylindrical roller having a length greater than its diameter.

8. A lift truck, comprising,

a frame,

a pair of stationary, outer uprights fastened to said frame in an approximately vertical position,

a pair of inner, movable uprights longitudinally extensible with respect to said outer uprights,

a load carriage movable along said inner uprights,

means for raising said carriage with respect to said inner uprights and .for raising said inner uprights with respect to said outer uprights,

said means including a portion of said carriage which is positioned to engage a portion of said inner uprights as said carriage reaches the top of said inner uprights,

a first member including a generally cylindrical sleeve portion formed with a radial aperture therethrough and rigidly fastened to said inner uprights with the cylindrical axis approximately horizontal,

a second member including a generally cylindrical hub portion formed with a depression in the cylindrical surface thereof and positioned within said sleeve portion of said first member with said depression axially aligned with said aperture, said second member including a first radially extending fork having two axially aligned tines,

a third member including a generally cylindrical sleeve portion formed with a depression in the inner surface thereof and positioned surrounding said sleeve portion of said first member with said depression axially aligned with said aperture, said third memher including a second radially extending fork having two axially aligned tines,

said second member having a reference position defined as that angular position at which said depression in said hub portion is angularly aligned with said aperture,

said third member having a reference position defined as that angular position at which said depression in said inner surface of said sleeve portion is angularly aligned with said aperture,

each of said forks being angularly positioned to be approximately horizontal when its associated member is in its reference position,

stop means for limiting the relative rotation of said members,

a locking element positioned principally within said aperture and having a radial dimension greater than the thickness of said sleeve portion of said first member but not greater than said thickness plus the depth of one of said depressions so as to necessarily extend into one of said depressions, whereby but one of said second and third members may be displaced from its reference position at any one time,

a first stud fastened to said outer uprights and positioned so that, with said inner uprights completely lowered and said second member in its reference position, said first stud extends between the horizontally extending tines of said first fork, whereby said second fork is urged downward there-by locking said inner upright-s to said outer uprights, and

a second stud fastened to said load carriage and positioned to enter the space between the tines of said second fork as said carriage approaches the upper end of said inner uprights and to raise said second fork to a horizontal position substantially as said portion of said carriage engages said portion of said inner uprights,

whereby as said means raises said carriage, said carriage raises said inner uprights and allows said first :fork to rotate downward thereby releasing said first stud and said outer uprights simultaneously locking said car-riage to said inner uprights.

9. Apparatus according to claim 8 in which said aperture in said first member is axially elongated to form a slot and in which each of said depressions is axially elongated to form a groove and in which said locking element is a cylindrical roller having a length greater than its diameter.

10. A lift truck, comprising,

a frame,

a pair of stationary, outer uprights fastened to said frame in an approximately vertical position,

a pair of intermediate, movable uprights longitudinally extensible with respect to said outer uprights,

a pair of inner, movable uprights longitudinally extensible with respect to said intermediate uprights,

a load carriage movable along said inner uprights,

hoist means including a crosshead for raising said load carriage with respect to said inner uprights, for raising said inner uprights with respect to said intermediate uprights, and for raising said intermediate uprights with respect to said outer uprights,

said means including first and second portions on said crosshead which are positioned to engage corresponding portions on said inner and intermediate uprights respectively and to raise said inner and intermediate uprights by upward movement of said crosshead in excess of first and second predetermined amounts respectively above a lowermost position,

said means also including a portion on said carriage which is positioned to engage a corresponding portion on said inner uprights as said carriage reaches the top of said inner uprights,

first and second latch elements, each comprising,

a first member including a generally cylindrical sleeve portion formed with a radial aperture therethrough,

a second member including a generally cylindrical hu-b portion formed with a depression in the cylindrical surface thereof and positioned within said sleeve portion of said first member with said depression axially aligned with said aperture, said second member including a first radially extending fork having two axially aligned tines,

a third member including a generally cylindrical sleeve portion formed with a depression in the inner surface thereof and positioned surrounding said sleeve portion of said first member with said depression axially aligned with said aperture, said third member including a second radially extending fork having two axially aligned tines,

said second member having a reference position defined as that angular position at which said depression in said hub portion is angularly aligned with said aperture,

said third member having a reference position defined as that angular position at which said depression in said inner surface of said sleeve portion is angularly aligned with said aperture,

each of said forks being angularly positioned to be approximately horizontal when its associated member is in its reference position,

stop means for limiting the relative rotation of said members,

a locking element positioned principally within said aperture and having a radial dimension greater than the thickness of said sleeve portion of said first member but no greater than said thickness plus the depth of one of said depressions so as to necessarily extend into one of said depressions, whereby but one of said second and third members may be displaced from its reference position at any one time,

said first member of said first latch mechanism being rigidly fastened to said inner uprights with the cylindrical axis approximately horizontal,

said first member of said second latch mechanism being rigidly fastened to said intermediate upright with the cylindrical axis approximately horizontal,

a first stud fastened to said outer uprights, for cooperation with said first latch mechanism, and positioned so that, with said inner uprights completely lowered and said second member in its reference position, said first stud extends between the horizontally extending tines of said first fork,

whereby said second fork is urged downward thereby locking said inner uprights to said outer uprights,

a second stud fastened to said crosshead, for cooperation with said first latch mechanism, and positioned to enter the space between the tines of said second fork as said crosshead rises and to raise said second fork to a horizontal position substantially as said first portion of said crosshead engages said portion on said inner uprights,

whereby continued upward movement of said 1 crosshead raises said inner uprights and rotates said first fork downwardly thereby releasing said first stud and said outer uprights and simultaneously locking said crosshead to said inner uprights,

a third stud fastened to said load carriage, for cooperation with said first latch mechanism, and positioned to enter the space between the whereby continued upward movement of said crosshead raises said carriage which in turn raises said inner uprights above said crosshead, simultaneously rotating said second fork downwardly thereby releasing said second stud from said second fork and latching said third stud and said carriage to said inner uprights,

a fourth stud fastened to said outer uprights, for

cooperation with said second latch mechanism, and positioned so that with said intermediate uprights completely lowered and said second member in its reference position, said fourth stud extends between the horizontally extending tines of said first fork,

whereby said second fork is urged downward thereby locking said intermediate uprights to said outer uprights, and

a fifth stud fastened to said crosshead, for cooperation with said second latch mechanism, and positioned to enter the space between said tines of said second fork as said crosshead rises and to raise said second fork to a horizontal position substantially as said second portion on said crosshead engages said portion on said intermediate uprights,

whereby continued upward movement of said crosshead raises said intermediate uprights and rotates said first fork downwardly thereby preleasing said fourth stud and said outer uprights and simultaneously locking said crosshead to said intermediate uprights.

11. Apparatus according to claim 10 in which said aperture in said first member of each of said latches is axially elongated to form a slot and in which each of said depressions is axially elongated to form a groove and in which said locking element is a cylindrical roller having a length greater than its diameter.

References Cited UNITED STATES PATENTS 2,501,581 3/1950 Rieger 292-252 3,082,239 3/1963 Hahn 339-918 3,221,840 12/1965 Weinert 18 -9 EVON C. BLUNK, Primary Examiner.

H. C. HORNSBY, Assistant Examiner. 

1. A LATCH MECHANISM, COMPRISING, FIRST, SECOND AND THIRD MEMBERS INCLUDING GENERALLY CYLINDRICAL PORTIONS POSITIONED CONCENTRICALLY WITH FREELY SLIDING FITS FOR RELATIVE ROTATION ABOUT THEIR COMMON AXIS WITH SAID FIRST MEMBER INTERPOSED BETWEEN SAID SECOND AND THIRD MEMBERS, SAID FIRST MEMBER BEING FORMED WITH AN AXIALLY ELONGATED RADIAL APERTURE OF SLOT, SAID SECOND AND THIRD MEMBERS EACH BEING FORMED WITH A GROOVE IN THAT SURFACE ADJACENT TO SAID FIRST MEMBER AND AXIALLY ALIGNED WITH SAID APERTURE, SAID SECOND AND THIRD MEMBERS EACH HAVING A REFERENCE POSITION DEFINED AT THAT ANGUALR POSITION AT WHICH ITS GROOVE IS ANGULARLY ALIGNED WITH SAID APERTURE, AND A CYLINDRICAL ROLLER POSITIONED PRINCIPALLY WITHIN SAID APERTURE AND HAVING A DIAMETER GREATER THAN THE THICKNESS OF SAID FIRST MEMBER BUT NO GREATER THAN 